Need Help reloading 7.62

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T6nut

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new here so excuse me if this has been covered. I built up a AR-10 and need help with the reloading data. it is a special build and the barrel has requirements. it was chambered for 7.62 x 51 using 168gr SMK HIBT and Varget powder. Can anyone give me some Min and Max loads to start my build up data?? "Powdermonkey" i read your post a while back and if you are here i know you are loading this.. thanks in advance for any help.

jcw
 
I don't beleive it is possible to build up a rifle to use a specific powder.

So you are already off the rails there with your question.

Hodgdon sells Varget powder.
Hodgdon provides tested load data for .308 Winchester.

So go there to get your tested data.

http://www.hodgdonreloading.com/data/rifle

rc
 
it is a custom made match barrel and the maker needed the upper, the bullet to use, the powder and the brass (lapua) and he built the barrel and twist for that to give me best acc at 700 yds. it's chambered for the 7.62 x 51 so i don't want to mix 308 win data.
 
The 7.62x51 is a .308 Win. so I'm not sure why you are saying something about mixing data??? It's just a differently if talking about the same cartridge.
 
Well if you had to provide a loaded cartridge to the builder then why don't you know what the powder charge weight was?
 
he recommended Varget but my books don't show data for varget. 7.62 service data for a gas gun is diff than 308 win bolt data don't want to make a mistake.
 
Since you already decided we are wrong why are you still asking our advice?

I hope you find what you are looking for but I guess I can't help you.
 
Here's the simple answer, there isn't any difference between a .308 Win cartridge and a 7.62x51 cartridge other than the powder charge being appropriate for a gas operated rifle.

There is no such thing as a 7.62x51mm reloading die set, there are only .308 Win dies. The only parameters that you can adjust for the AR10's barrel is the overall cartridge length, the head space dimension of the case, and the powder type and charge, all of those parameters are controlled during the process of building the cartridge by how you setup the dies and measure the powder charge. You make those choices by adjusting the same equipment that is used to reload a .308.

It sounds to me like the builder used a specific turn rate and probably cut the chamber to 7.62x51mm specs which means that the throat is a little longer than a typical .308 Win and the head space of the chamber is a little longer than a .308 Win chamber.

For an AR10 I'd suspect that the max chamber pressure is similar to military specs so I would try to keep the chamber pressure to no more than around 60,000 PSI. A reasonable range of powder charge weights using Varget would be around 41 grains to 43 grains. The max powder charge would be around 45 grains but that would be pushing an AR pretty hard and I wouldn't recommend going that high.
 
Start with 40 grains of Varget behind that Sierra boattail, and work up from there. That will start you out around 2400 fps.

I think the gun builder is blowing smoke up your.....barrel. The chambers for 7.62x51 and .308 are essentially the same. It's the cartridge case that's different, 7.62 milspec cases being thicker and are loaded to lower pressures. Also, loading for a semi is a bit different than for a bolt gun, you can generally go hotter with the bolt gun. I load for a M14 and for a .308 bolt gun. I full size for the semi each time, but I neck size twice before full sizing the .308 brass. I can get more loads per case before seeing signs of impending case failure with the bolt gun, while using heavier powder loads, and I don't have to worry about case feeding issues in the bolt gun like I do with the semi. Did your builder recommend a small base die for the chamber? Some semi's need to be small base-sized so they will reliably feed. I can use up to 43.2 grains of Varget in my bolt gun before starting to e pressure signs, but I don't use Varget with my M14 loads. I'm not sure how the action in an AR10 handles hotter loads, but I have to watch for op rod damage with hot M14 loads. I use H4895 or IMR 4895 with my 7.62 loads

Even if the builder/gunsmith, whatever, says to use only such-and-such, you owe it to yourself to try some different loads. H4895 or IMR4895 works well in the .308/7.62, and 178's have a better BC than 168 grain bullets, so for the longer range they'll usually fly better.

What's the barrel length on your rifle, and what twist?
 
Actually the chambers are different, not by much but they are different.
Not all commercial cases are thinner walled or have less volume than military cases.
Not all commercial cartridges have higher pressures than military cartridges.
 
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7.62 service data for a gas gun
Click to expand...

Usually is specific data for the M1 family of rifles. They have different max pressure and more important is the pressure curve, due the the op rod operation in those rifles. Too high pressure causes problems, to quick/slow of a spike in pressure cause problems. Those issues are more specific to that family of rifles.

Those issues do not exist in the AR family because there is no op rod. But with any rifle, with any powder/bullet combo, start at the min and work up to find the max for YOUR rifle, it will let you know if you watch for the signs. I have had couple rifles that reached their max 2 grains below any published data. Published data is not an absolute, it is a set of guidelines to give you a starting point.

I am also curious as to the barrel manufacturer, length, and twist rate.
 
awesome, this is where i was hoping to go with this. thanks Macgrumpy,bangswitch,and otrman. this is giving me a place to start my workup. to answer some of your questions: the reloading dies ARE diff. i have to use the RCBS .308 win SB T/C die set #15507 group AR. not standard .308 win. the upper is a heavy bolt "JP" and the barrel is a custom "JB" competition Match unfluted 22". this guy makes barrels for a number of the competition shooters. he suggested the 168 first but said up to 175 will work fine. twist if i remember correctly is 1 in 10 (will check paperwork to make sure, it might be slightly odd) up to me to dial it in for the gun. i just didn't have any data for the varget to start. i'll start at 40 and work up. once i have it then will try H4895 and IMC 4895. any ballistic data on the varget would be great as i will need that to turn in with the scope for new range cams. i know that "powdermonky" was using 43.2 varget, 168 HIBT, Fed Gold match primer, trimmed Rem brass. (i'm using lapua). i just didn't have the Min and Max numbers. thanks again this helps...
 
While the ARs have no op rod they do have a design limitation that is reflected by the max pressure that NATO specifies for the 7.62x51mm cartridge. The NATO spec is a little over 60,000 PSI (60,190 PSI to be more specific) while the SAAMI (American civilian safety authority) specifies 62,000 PSI. These organizations actually measure the pressure using slightly different procedures which probably accounts for most of the pressure specification difference.

A powder charge weight of a little over 45 grains of Varget would produce a max pressure that is pretty close to that NATO max but this is when knowing the pressure curve is really important. As you get closer to the max chamber pressure value, how the powder burns becomes more important, specifically when/where the pressure spikes. Barrel profiles usually become thinner as the bullet moves toward the muzzle and the powder's pressure curve should follow the barrel's profile - in other words, the highest pressure should occur where the barrel is the thickest. If the pressure curve (pressure vs. time or pressure vs. distance along the barrel) indicates that the pressure peaks beyond the thickest part of the barrel you might see bad results. For an AR you should also need to know that the pressure is in the appropriate range at the gas port, too high of pressure can cause bolt and bolt carrier problems (boom?) and too low can cause cycling problems.
 
I don't see where that die set is any different than a standard .308 small base die except for the fact that the set also includes a taper crimp seating die. That's nothing unique to the AR, it could be used for any other .308. Other manufacturers make a crimping die but it's usually a separate die that is used after bullet seating. The dimensions of the resizing die are the same as any other small base .308 die.

And no, you don't HAVE to use that die set, it's just recommended by those that like to crimp their cartridges. Crimping is actually unnecessary in most situations for the average civilian shooter. If the barrel is custom made for the tapered crimp that the seating die produces then I'd say that it is better to use that specific die set, but otherwise any .308 die set will work for your rifle. As a matter of fact, I'd bet that you could test cartridges reloaded with that die set and and any other die set and you'd be hard pressed to see any real difference in performance.
 
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it may be an RCBS issue. was told to use the #15507 SB T/C not the reg .308 win to insure proper feeding.
 
Hornady reloading manual has a sections specific for service rifles in 5.56 and 7.62/308.

Sierra also has a section dedicated for 5.56 AR pattern rifles.

My recommendation would be to pick up a copy of both and read. That's what I did and it really helped me.....a long with the sage advice I've received here at THR
 
T6nut said:
it is a custom made match barrel and the maker needed the upper, the bullet to use, the powder and the brass (lapua) and he built the barrel and twist for that to give me best acc at 700 yds. it's chambered for the 7.62 x 51 so i don't want to mix 308 win data.
Click to expand...
He's blowing smoke up your butt.

7.62X51 is .308. Use .308 data. Any of it.

He cut a chamber using a reamer cut to SAMMI specs. It is probably a tight chamber, with short throat ("Target" chamber), but it is still just a .308 rifle.

The twist only needs to be "fast" enough to stabilize a 168 Gr Match bullet (As heavy as you need at 700 yards). Nothing special about that.

Buy some 168 gr match bullets, some suitable primers, some Varget, IMR 4895, or IMR 4064, or RL 15 (Or a couple of others), start low, and work up a good load.

Nothing special about it. You match loads to the rifle. A rifle is either "match" quality, or it isn't.

it may be an RCBS issue. was told to use the #15507 SB T/C not the reg .308 win to insure proper feeding.
Click to expand...

Crimping, taper or roll, isn't going to make a rifle feed if it won't feed with no crimp. Maybe he is concerned you will over crimp wit the roll crimp and buckle the shoulder, but you can do that with the taper crimp as well. Just more jaw jacking I imagine.
 
Yep, the smoke is flowing... a 1:10 twist is pretty standard for a .308. I have an AR-type rifle in .308 (Rock River LAR-8) and it's quite happy with any bullets from about 150 grains on up. It absolutely LOVES the Nosler 155 grain Competition bullets and I've had the best luck with 45.0 grains of IMR-4064, which my chronograph says is 2846 FPS. Sub MOA groups.

You may find that your rifle will shoot many different types of bullets quite well.
 
all good info. this will get me started. will report back with results

thanks to all for the help
 
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